REP10784

• Permit No: M1988112
• IBM Index Class Name: Report
• Doc Date: 7/14/1995
• Doc Name: APPENDIX B.2 CPT PROBES
• Media Type: D
• Archive: No

' In all of the soundings, the CPTs were terminated when the drill rigs hydraulics were not able to
advance the cone any further.
2.2 Downhole Seismic Testing
The equipment and procedures used for determining shear wave velocities were in general as reported
by Robertson et al, 1992. The procedure was incorporated within the CPT and conducted when
penetration was stopped to add additional push rods. At the end of the second push and at one meter
intervals thereafter, shear wave velocity measurements were made. The CPT rods are one meter long,
and therefore accurate depth irnervals were ensured by always pushing the cone rods one meter.
Before taking shear wave velocity measurements, the rods were decoupled from the drill rig to
min;mi~e background noise.
' Shear waves were generated by striking an auger which was set in place by the drill rig. This provided
excelled coupling of the shear source to the ground surface. The auger was offset hotizontaIIy from
the cone rods at varying distances, which were recorded. This offset was accounted for in the
' velocity calculations.
A friction reducer was used to reduce the friction between the soils penetrated and the cone rods
behind the cone. The particular reducer used is oversized compazed to conventio~i reducers to
facilitate the decoupling of the cone rods from the sor7s in an effort to produce a high quality signal
and high signal to noise ratio.
The auger was struck lightly for shear wave generation using a l O lb. sledge hammer in a horizontal
direction, parallel to the active axis of the seismic receiver. Each wave was inspected and the
' . procedure was repeated if necessary. An electrical contact trigger between the auger and the hammer
produced accurate triggering times which allowed for the accurate timing of S wave markers.
' After each wave trace was recorded, inspected and saved, the traces were examined on a digital
oscilloscope to select signal markers for interval time computations. The field technique employed
' for determination of shear wave velocity is known as the pseudo interval method.
The shear wave receiver used was a horizontally active geophone located in the body of the
1 piezocone. The geophone is located 0.2 meters behind the cone tip. This offset is accounted for;n
all calculations. The oscilloscope sampled at a frequency of 20 kHz (ie: 20,000 samples per second).
In general, 5,000 sample points were taken per wave trace. The AJD resolution of the oscilloscope
used was 8 bit. Because shear wave signals attenuate significantly in soils, the input sensitivity (gain)
of the receiver was increased with depth to maintain acceptable signal resolution.
2.3 SPTs Energy Calibration Testing
' Three borings were drilled near three of the CPT holes. These borings were used for correlation of
the CPT results with samples of the tailings. The samples of the tailings were taken using a 3-inch
OD split spoon sampler. The sampler was driven in 24 inch increments using the 140 Ib. auto
' CoNerkC.lxG Z pmvc. Colorado